Recently Google initiated and proposed a new congestion control for Transmission Control Protocol (TCP) flows. The new congestion control known as the BBR is based on measuring two parameters that characterize a path, namely, Bottleneck Bandwidth and Round-trip propagation time (BBR). In BBR, a sender measures the bottleneck bandwidth and Round Trip Time (RTT) via received acknowledgments (ACKs). Data inflight of the sender is essentially based on the product of the measured bandwidth and RTT. In addition, BBR paces the sending rate using the in-flight data amount and the RTT.
Conventional TCP congestion control for the in-flight data of the send is based on a window size determined by both the sender and the receiver. The sender shrinks the window size if it sees missing ACKs; ACKs that are presumably due to packet drops on the path as a result of congestion. Based on such a feature of the sender, intentionally dropping a packet at an intermediate node could alleviate congestion on the path. Random Early Detection (RED) is based on such a mechanism. US Patent Publication Number 2013/0136000 incorporated herein by reference in its entirety discloses a conventional teaching.
BBR differs from conventional TCP congestion control in the sense that it is not sensitive to a packet drop. Although BBR alters a sending rate based on received ACKs, unlike conventional TCP congestion control, randomly dropping a single packet does not affect BBR's sending rate. In contrast, conventionally, a missing ACK could essentially cut a transmission rate of the sender by half. In the present teachings, data flows using BBR are referred to as BBR traffic while data flows not using BBR are referred to as non-BBR traffic.
A High Throughput Satellite (HTS) may use a congestion control scheme such as RED. RED is applied at an Internet Gateway (IPGW) of the HTS to flow control the incoming traffic to the Performance-Enhancing Proxy (PEP). The IPGW randomly drops packets of all flow sessions to push back TCP traffic during congestion. This is assuming all TCP sources follow the conventional congestion control. However, when a significant amount of BBR traffic is received and ACKed by the IPGW, during congestion, the BBR traffic could accumulate at the IPGW (since random dropping would not affect its sending rate) and cause issues to non-BBR traffic. As BBR traffic does not push back due to a packet drop, RED would be triggered more frequently when BBR traffic takes more buffer space, resulting in less non-BBR incoming traffic, and consequently lowering a throughput of non-BBR flows compared to BBR flows.